The present invention relates generally to the field of portable tools, and more particularly to an output shaft locking mechanism for a trimmer.
In a cutting tool such as a brush cutter, a trimmer and/or the like, a rotatable cutting element is mounted in a positive interlocking or force-actuated manner, on an output shaft. The cutting element, such as metal or plastic blades, a line head or line carrier, may need to removed for various reasons. However, because removing it typically requires twisting either the cutting element or a fastener with respect to the axis of the output shaft, the output shaft must be typically held.
Many power tools include locking mechanisms for stopping rotation of an output shaft so that a cutting element or other tool element may be attached. However, these mechanisms suffer from various shortcomings. They tend to be relatively complex, which increases cost of assembly and renders them more susceptible to malfunction, and are sometimes not easy for an operator to use.
The present invention concerns an improved output shaft locking device for a trimmer or similar tool, which finds particular advantage on a power tool that includes a gear box with an output shaft, to which a cutting element is mounted.
A representative example of an embodiment of a locking mechanism according to the invention includes a pin or pin-like element that translates within a channel formed on the outside of a gear box housing. The pin does not penetrate the housing, thus avoiding another opening in the housing that must be sealed. Rather, when the pin is extended below the gear box housing to locking position, it interferes with a rotating element (other than the cutting or working element) that extends outwardly from, and rotates with, the shaft. Thus, the direction of translation can be generally characterized as parallel to the output shaft, but it need not be strictly so. The invention may be thus advantageously used on a vegetation cutting tool that already has a dust cap to keep dirt and other debris away from the seal between the output shaft and gear box, or similar element mounted on the shaft. Furthermore, the pin may be positioned to engage the non-working element some distance from the axis of rotation of the output shaft and any lateral force applied to the pin is distributed along the length of the channel. The gear box and locking mechanism will thus suffer less stress due to transfer of the torque from the output shaft to the pin, such as when the operator is attempting to remove the cutting or working element, or in the event an operator applies attempts to lock the output shaft while it is still rotating or while power is still being applied.
In order to extend the pin manually, the pin and channel are sized to reveal a top portion of the pin that may be depressed. In a retracted position, the pin is withdrawn into the channel far enough to avoid interfering with the rotation of the non-working element. Biasing the pin with a spring or similar element so that it automatically retracts it into the channel when it is not depressed reduces the risk that an operator attempts to run the tool with the shaft in a locked position, as manual force must be applied to the pin to keep it extended.
Other aspects and features of the invention will be apparent to those ordinarily skilled from the following description of specific embodiments of the invention in conjunction with the accompanying figures.